The present invention is directed to switchgear cubicle racking mechanisms; and in particular hand-operated cranking mechanisms which accomplish racking movement of switchgear draw-out units and mechanical displays which indicate position of draw-out units within cubicles.
Rackable switchgear draw-out units, such as draw-out vacuum circuit breakers are commonly used in the electrical distribution and control fields. The draw-out unit is housed within a cubicle and connected to a busway system within the cubicle for transmission of electrical power. The draw-out units can be removed from the cubicle by translation on fixed, non-steerable but rotatively-mounted wheels or rollers, after power to the cabinet is shut down and appropriate safety measures well known in the art are taken to inhibit the likelihood of injury to service personnel.
Translation of the draw-out units within the cubicle is accomplished with a racking mechanism. A known example of a switchgear cubicle with a draw-out unit racking mechanism is sold by the assignee of the present application, Siemens Energy & Automation, Inc., through its Electrical Apparatus Division, located in Raleigh, N.C., U.S.A., under the designation, "Type GM Switchgear".
In the known switchgear, a racking screw mechanism having acme-type threads is affixed to the cubicle on sleeve bearings. Rotation of the screw mechanism translates a drive block having a cammed toggle attached thereto. The toggle urges against a racking block affixed to the draw-out unit, such as a vacuum-type circuit breaker, in order to cause translation of the draw-out unit.
In the known switchgear racking mechanism, the screw mechanism was rotated by way of a crank handle having a female socket portion which engaged a male socket portion constructed on the screw shaft. In order to engage the mating socket drive portions, the previously known switchgear required constant exertion of inwardly directed axial force by the operating technician, because the crank had to be continually biased against a spring loaded racking shield in an axially inwardly direction relative to the screw shaft while turning the crank. The racking shield only partially encircled the screw shaft and spring loading of the shield was accomplished by way of a plurality of offset, tensioned springs.
The existing racking shield of known switchgear is a relatively complex mechanism which does not afford smooth, relatively constant inward tension by the crank operator in order to turn the racking screw.
It is desirable to know the racked position of the switchgear racking unit. Known racking unit position indicators utilize a continuous tape with indicia marking calibrated to correspond to the position of the racking unit. The tape is guided on rollers and a linear tensioning device is utilized to maintain tape tension around the rollers.
Known tape position indicators have been positioned laterally along a side face of the racking unit, so that they have been visible only from close to floor height. An operating technician would have had to bend down to read the indicator and would not have been able to maintain a normal standing position for cranking the unit. Hence, the operator would have had to crank, cease cranking in order read the indicator, and if necessary resume cranking in order to position the racking unit to the desired racked location--for example a test or disconnect position. The operating technician would have had to repeat the guessing process as often as necessary to place the racking unit in the desired position. Also, if the door of the cubicle were open during the racking procedure, the technician would have had to bend down near floor level to read the tape indicator.
It is an object of the present invention to eliminate the need to exert continuous inwardly-directed biasing force against the switchgear racking mechanism crank to enable racking screw turning, so as to translate the switchgear draw-out unit.
It is another object of the present invention to simplify the racking shield and related spring mechanism, so as to provide more uniform inwardly directed axial pressure by a crank operator against the racking screw during engagement of mating socket portions.
It is yet another object of the present invention to reduce manufacturing effort and cost of the racking shield and related spring mechanism of a switchgear racking unit.
Another object of the present invention is to create a racking unit position indicating tape system which allows an operating technician to determine a rackable switchgear draw-out unit position within the cubicle from eye level, in a normal cranking position, so that the technician can determine the position while simultaneously cranking the racking mechanism.
An additional object of the present invention is to enable an operating technician to determine at least one selected position of the draw-out unit while the cubicle door is open.